The present invention relates to a threading tool for the production of threads, in particular for the cutting of internal threads.
The term “threading tool” is intended to include both thread-cutting tools, e.g. screw taps or thread milling cutters which cut chips, and thread-forming tools, so-called thread formers, inasmuch as they are provided in each case for the production of internal threads. In both cases, the tool is introduced into an already existing core bore or core hole bore in order to form the internal thread.
During thread “forming” (as opposed to “cutting”), the thread is moulded into the core bore, i.e. there is a softening of the material (plastic deformation), and the material flows around the teeth of the thread former and forms the characteristic thread profile. Thread forming is a reshaping manufacturing process without the formation of chips. Moreover, through the deformation a smoother and stronger surface can mostly be achieved, as the deformation is associated with a compacting of material.
During tapping, the threading tool, in the form of a thread-cutting tool, tool is screwed into the bore at a rate precisely matched to its speed, while the cutting teeth, which are arranged in several essentially parallel-running groups (called hob-blade inserts), cutting the threads. With a single-flight thread, the distance between the cutting teeth, arranged behind one another in axial direction, of a group corresponds exactly to the thread pitch and/or the height of a thread.
In general, the threading tool has a shank or a shank part and a threading part or cutting edge section. The threading part has spiral threads running round the peripheral surface. In a tap, the threads are interrupted by longitudinally extending passages in the form of flutes.
The threading part of threading tools consists in most cases of a gate and a guide part. The gate is provided with a tapering cross-section and carries out most of the chip cutting and/or the deformation. The guide part serves essentially only for guiding and has no, or only a very slight, taper.
These tools are often operated with a coolant or a cooling lubricant which is intended to reduce the friction between tool and workpiece, remove process heat from the contact point, ensure a good chip transport and achieve a good surface quality. The coolant can be supplied in different ways, but is usually removed again via the flutes. To remove the coolant or cooling lubricant, the threads of a thread former are therefore also interrupted in the axial direction by axial passages in the form of grooves, so-called oil grooves. However, as the oil grooves of a groove former serve merely for the removal of the coolant and not the removal of chips, the oil grooves can be developed less deep, as compared with the flutes of thread cutting tools, and optionally also less wide.
With threading tools, the supply of coolant or cooling lubricant is not easy because, during the cutting process, the tool is almost completely surrounded by the material to be worked. Thus the blades formed by the threading part are in general not accessible from the outside. In order therefore to conduct the required coolant to the chip cutting location, two different methods and tools are known in the state of the art.
In the first method, the coolant is supplied axially. This means that there is an axially-running coolant through bore in the centre of the tool. If this tool is introduced into a core bore designed as a bottom or blind hole, the coolant emerging from the coolant channel flows firstly into the bottom hole. After the bottom hole is filled with coolant, the coolant continuing to flow through the axially-running coolant channel forces the coolant past the tool and through the flutes or oil grooves out of the bottom hole. This results in an effective removal of the chips produced during the chipping process.
It is obvious that such threading tools can be used only with bottom hole threads, as with through holes the coolant would not reach the blades but simply flow through the through hole.
In the second method, there is a radial coolant supply. Although the tool in this case also has a central bore which forms an axially running coolant channel, this channel does not extend to the end surface of the tool. Therefore either a blind hole bore is provided or initially a through bore is produced which is then closed again at its end surface. In addition radial bores are provided in these tools, extending from the circumferential surface of the tool to the central axially running coolant channel.
Typically the radial bores are arranged such that each of them connects the centrally running coolant channel to a flute and/or oil groove.
In the known tools, the radially running coolant bores do not run perpendicular to the axial bore, but are inclined forwards, i.e. towards the end surface of the tool. There are essentially two reasons for this. Firstly, the coolant can thereby be conducted in the direction of the gate, as in this area, as already stated, most of the chip cutting and/or deformation and thus also most of the heat development occurs. Secondly, the attenuation of the tool core cross-section, which is necessarily associated with the provision of radially running channels, is thus reduced.
However, considerable disadvantages are associated with both previously known versions. With the axial coolant supply, the scope of application is restricted to bottom hole threads, because with through holes the coolant would not reach the blades.
Although the version with the radial coolant supply is very versatile, it is very elaborate and therefore expensive, as the production of the generally very small radial bores is possible only by milling in combination with drilling or erosion.
In addition, the radially running bores, even if they are inclined in the direction of the end surface of the tool, lead to a considerable attenuation of the cross-section and thus of the tool. In the worst case, this can lead to a tool fracture in the area of the radial bores.
Moreover, with the customarily used inclination of the radially running coolant bores, the coolant jet is directed against the chip flow. This necessarily leads, with threaded cutting tools, to an inadequate removal of chips. In addition, the supply of cooling lubricant to the guide part is insufficient.
Starting from this state of the art, the object of the present invention is to provide a threading tool with a threading part having at least one flute or oil groove and an axially running cooling channel which extends essentially to the end surface of the tool, which is easy to produce, has a long tool life, i.e. with which in particular the danger of tool fracture is clearly reduced, which can be used both when tapping a through hole and with a bottom hole thread, and with which the supply of the coolant or the cooling lubricant is such that a chip flow is not hindered, but supported, and with which the coolant or cooling lubricant sufficiently supplies both gate and guide part.